1. Field of the Invention
The field of art to which this invention pertains is light-sensitive compositions and products made therefrom. In particular, the pertinent prior art can be found in those areas dealing with photo-sensitive compositions or photo-sensitive substances made therefrom. Printing or imaging plates in general or presensitized lithographic plate art or photo-sensitive polymeric art will be the most relevant.
2. Description of the Prior Art
Photo-sensitive compounds which are polymeric substances are well known in the art. In particular, these substances can be used in a wide variety of photochemical processes. For example, they can be placed on resilient surfaces and be used for many types of printing plates and particularly for lithography or offset printing, or they can be used for the production of printed circuit boards by chemical milling and etching. The claimed compositions are particularly suitable for use as photopolymers in light-sensitive coatings for lithographic plates or in other systems such as relief plates, general resists, silk screens, etc. They may also be used in printing inks or other light-sensitive coatings.
In a commercial sense, and in particular in the production of lithographic plates, a light-sensitive coating is generally placed on a backing member which in many instances is a metallic substance. A negative or other means to control light exposure to the plate is utilized to selectively cause the areas of the plate struck by a light to become differentially soluble with respect to a solvent, which is subsequently used to flush the non-exposed substance from the backing plate. The image area or the area which has been subjected to light becomes receptive to inks while the non-image area or the area which has not been contacted with light, and which typically has been washed away by a suitable solvent, is not receptive to ink. Therefore, the printing of an object can be accomplished by contacting the developed plate with a particular ink which adheres only to the areas of the plate which have been struck by light. Thereafter, the plate can be contacted with a transfer roll or directly with paper for transfer of ink from the image areas.
Early in the prior art such light-sensitive plates were prepared for immediate use. Because of the nature of the light-sensitive materials utilized their storage or shelf like was substantially reduced when subjected to the atmosphere or to humidity or to extraneous light in relatively small quantities. An improvement over these substances is now known. Many of the presensitized lithographic plates utilized in industry are made of such light-sensitive materials that they are virtually indestructible when contacted with air or moisture, but when contacted with certain wavelengths of the electromagnetic spectrum become substantially instantaneously reacted, thereby rendering a light sensitized product.
The present invention is suitable for use in presensitized lithographic plates or in other areas of photopolymeric chemistry wherein a material which when contacted with certain wavelengths of the electromagnetic spectrum becomes polymerized or insolublized with respect to a solvent and which thereafter can be utilized, for instance in the lithographic plate field, as image-receptive areas. In another instance, the particular photosensitive compounds claimed herein, can be utilized in conjunction with a certain polymeric system so that when contacted with a certain spectrum of electromagnetic radiation the polymeric system can be degraded, thereby rendering a material which can decompose upon contact with light. In particular, the latter application has been of interest in the packaging industry to help reduce littering problems. For instance, such a polymeric system might upon exposure to sunlight become very brittle through a photoreaction enabling it to be more easily weathered by the elements. The use of our particular components in such a polymeric system can allow the container, which when subjected to various quantities or various spectrums of electromagnetic radiation can decompose in a predictable manner, thereby reducing the threat of pollution from containers indiscriminately disposed of.